Hydraulic lash adjuster



Feb. 3, 1959 M. v. DADD HYDRAULIC LASH ADJUSTER Filed Nov. 12, 1957 IN VEN TOR. fiozzz' mam? A T TORNE Y wins Patented Feb. 3, 1959 iiice HYDRAULIC LASH ADJUSTER Morris V. Dadd, Ada, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November-12, 1957, Serial No. 695,723 10 Claims. Cl. 123-90 This invention relates to poppet valve operating mechanisms for internal combustion engines and the like using rockers for transmitting valve opening and closing movements to and from the valve, and particularly to a hydraulic mounting for such a rocker which automatically adjusts its fulcrum to compensate for wear and other factors tending to affect the lash or operating clearance between the rocker and other parts drivingly associated with it. 1

One of the principal objects of the invention is to improve such mechanisms by arranging the rocker thrust to be applied to a dashpot having only a single leakdown path. In such prior devices of this type shown in U. S. Patents 2,785,666 to Evans and 2,718,219 to Chayne et 'al., dashpots are employed but there are two possible leakdown paths, one of which is intended to be sealed in order that the other will control the dashpot action. While it has been foundin certain applications of those prior devices that the use of such a seal will give satisfactory results, the seal nevertheless presents a potential risk of operational failure because in event of the seal breaking down the desired leakdown rate cannot be maintained.

Additional advantages in the present invention lie in elimination of tendencies toward binding of the telescopic parts of the dashpot, improved lubrication of the journaling and sliding surfaces and assurance that oilentrained air will be effectively vented from the device.

In contrast to the lash adjuster arrangements of the aforementioned patents, my invention envisages employ- ;ing a'dashpot plunger which is neither rigid with the rocker mounting stud nor serves directly to journal the :rocker, but which receives its thrust from a rocker bearing fixed stud extending through the rocker.

The invention will be more clearly understood from the following description, having reference to the drawing wherein:

Figure 1 is a transverse view through a portion of a V- type internal combustion engine incorporating a rocker hydraulic lash adjuster mechanism in accordance with the invention.

Figure 2 is an enlarged cross-sectional view of the lash adjuster mechanismand certain of its associated engine parts as shown in Figure 1.

Figure 3 is a sectional view through the dashpot assembly, taken subtantially on lines 33 of Figure 2, but showing a portion broken away to better illustrate the mechanism.

Referring now in detail to the drawings, there is shown an engine frame including a crankcase 1 of a conventional V-type having a cylinder head 2 for each bank. An engine driven cam 3 drives the tappets 4, each of which is connected to a push rod 5 and a valve rocker 6 to actuate a poppet valve 7. As shown, the rocker 6 is of generally upwardly presenting channel-like configuration and has its respective ends overlying the upper ends of the push 2 rod 5 and the stem of the valve 7, each of which protrudes above the cylinder head 2.

As most clearly shown in Figure 2, the rocker has its bottom wall spherically depressed to form a bearing surface 8 which surrounds an opening 9. Rigidly secured as by press fit in a hole provided therefor in the cylinder head 2 is a stud 10 which extends through the rocker opening 9 with sufficient lateral clearance to accommodate full rocking movements of the rocker in operation. Slidably embracing this stud is a ring-like bearing member 11 whose outer and lower periphery conforms to and journals the rocker bearing surface 8. Rigidly secured to and extending above the stud is a cylinder 12 of downwardly presenting generally cup shape. Attachment of the cylinder 12 to the upper end of the stud is illustrated in the form of a threaded connection 13 to a head 14 of the stud. It will be appreciated, however, that other means of such attachment may be used, and that the head 14 may instead be an integral part of the cylinder 12. In the arrangement shown, the upper or closed end wall 15 of the cylinder 12 cooperates with the cylinder bore 16 to form a dashpot for a slidably fitted plunger 17.

Means are provided for transmitting thrust from the rocker bearing 11 to the plunger in a novel manner which minimizes side loading and resultant tendencies of the plunger to bind in the cylinder bore 16. A platform member in the form of a circular plate 18 has a loose fit within the cylinder below the plunger and rests on a plurality of circumferentially spaced legs 19 extending loosely through drilled bores 26 in the head 14. These legs 19 are in the form of simple pins, non-integral with the platform member 18, and rest at their lower ends on the upper surface of the rocker bearing 11. Abutment between the platform member 13 and the lower end of the plunger 17 is confined closely to the plunger axis as by conically shaping the bottom surface 21 of the plunger.

Means are provided for introducing and trapping engine oil in the oil cushion chamber 22 between the plunger and closed end 15 of the dashpot cylinder. For this purpose, the cylinder end wall 15 is provided with an oil inlet port 23, below which is a check valve in the form of a ball 24 which is retained in operative position for closing the port 23 by a perforated cage member 25. A spring 26 operates to hold the cage 25 in place against the cylinder end wall 15 and also to bias the plunger outwardly of the cylinder into abutment with the platform member 18. Suitably secured to the upper end of the cylinder 12 and spaced externally from its end wall 15 is a cover 27 defining a reservoir 23 for oil under pressure to feed the cushion chamber 22. A drilled passage 29 extending longitudinally through the side wall of the cylinder connects with otherdrilled passages 30, 31 in the head 14 and stud 1G. The lower end of the stud passage 31 communicates with an oil gallery 32 which is supplied with oil under pressure from the engine lubricating system.

The internal surface 33 of the cylinder end wall 15 is inclined upwardly toward the oil inlet passage 23 at a sufficient angle relative to the cylinder axis to assure that the inclination of this axis from vertical (occurring when the lash adjuster is installed in the plane of one cylinder bank of a V-engine) does not result in creating a pocket for entrapment of air in the upper portion of the cushion chamber. Also in aid of venting air carried to tthe lash adjuster with the oil, a hole 34 is provided in theuppen most portion of the cover 27. Loosely fitting this hole 34 is a double check valve having a stem portion 36 substantially smaller than the hole 34 and upset at opposite ends to retain it in the cover while allowing sufficient axial movement to prevent both upset ends of the valve from simultaneously abutting the cover.

During operation, with each lift stroke of the cam 3,

its motion is transmitted through the tappet 4, push rod and rocker 6 to open the engine valve 7 against its return spring 37. The resultant upward thrust of the rocker against its bearing 11 is transmitted by the legs 19 and platform member 18 to the plunger -17. Resultant upward movement of the plunger is resisted by a rapid buildup of pressure of the oil in the cushion chamber 22, causing the ball check valve 24 to close. The sidable fit of the plunger in the cylinder bore 16, however, accommodates a slight leakage of oil from the cushion chamber downwardly past the plunger. This oil has freedom to drain down through the pin bores 2i) and the drain bore 20 and serves to lubricate both the rocker journaling surface 8 and the slidably engaged surfaces of the stud and bearing 11. After completion of the cam lift stroke and the tappet has returned to 'the base circle of the cam 3 the plunger spring 26 effects a re-expansion of the cushion chamber 22 to compensate for such foreshortening thereof as occurred during the lift stroke. The extent of such previous foreshortening is, of course, primarily that resulting from oil leakage, or leakdown, past the plunger. However, the re-expansion of the cushion chamber additionally compensates for such minute wear as occurs on the abutting thrust surfaces of the various parts in the valve train, as well as any change in their combined operative lengths resulting from thermal expansion and contraction of the parts. As this re-expansion of the cushion chamber 22 occurs, the oil pressure therein decreases sufliciently to allow the ball check valve to open so that oil under supply pressure from the engine lubricating system may flow into the chamber 22 from the reservoir 28. Upon start of the next lift stroke of the engine cam the cycle is repeated.

The above described arrangement of the downwardly presenting dashpot cylinder with its plunger movable upwardly therein under thrust from the rocker bearing 11 enables employment of the clearance fit between the plunger and cylinder bore 16 as the only leakdown path from the oil cushion chamber 22. Thus, the use of seals in a stud-mounted lash adjuster of this type is avoided. Also, the plunger thrust loading is confined axially thereof to insure against possible binding of the plunger in the cylinder which might result from any bending deflection of the stud or other causes, and the provisions for venting air from the cushion chamber and its reservoir 28 avoid any spongy action which would interfere with precise valve timing.

It is appreciated that various minor changes in the construction and arrangement of the parts will readily suggest themselves to those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined.

I claim:

1. In combination with a rocker having an opening extending therethrough in the thrust direction, supp-orting and journaling means for the rocker including a dashpot, a plunger movable inwardly of the dashpot in response to rocker thrust, a rocker bearing disposed oppositely of the plunger from the dashpot, thrust transmitting means extending between the bearing and plunger, and fixed supporting means for the dashpot extending through the rocker opening, each of said bearing and thrust transmitting means being guided by said fixed means between the rocker and plunger.

2. In combination with a rocker having an opening extending therethrough in the thrust direction; supporting and journaling means for the rocker including a fixed member extending through said opening; a dashpot facing the rocker and securing to the extended end of said member; a bearing defining the fulcrum axis of the rocker and embracing said member between the rocker and dashpot; said bearing being guided by said member for movement axially therealong; a plunger in the dashpot opposing thrust induced movements of the rocker and bearing; thrust transmitting spacer means between the bearing and plunger; means biasing the return of said plunger, spacer means, bearing and rocker when the rocker thrust is relieved; and means for supplying fluid to the dashpot inwardly thereof from the plunger.

3. In combination with a rocker for transmitting motion between oppositely reciprocating elements, rocker supporting means including a bearing journaling the rocker for oscillation about its fulcrum axis, a fixed member supporting and guiding said bearing for linear movement in response to rocker thrust, means rigid with said member and defining a bore on the opposite side of said bearing from the rocker, a plunger slidably fitting said bore and biased into thrust receiving relation with said bearing, a fluid chamber at the end of said bore most remote from said bearing, said chamber having an inlet, a check valve for said inlet accommodating fluid flow into said chamber and preventing fluid flow out of the chamber, and means for supplying fluid to said inlet for admission to the chamher when said check valve is open.

4. Supporting and journaling means for a rocker of the stud mounted type which has an opening extending therethrough in the thrust direction, comprising a fixed stud adapted to extend through the rocker opening,

' a rocker bearing telescopically embracing the stud and guided for axial movement thereby, a generally cupshaped cylinder facing and rigidly secured to the stud on the opposite side of the bearing from the rocker, a plunger sidably fitting the cylinder, thrust transmitting means extending between the bearing and plunger including a platform member within the cylinder having a plurality of legs resting on the bearing, said platform member and the adjacent end of the plunger having opposed surfaces in abutment with each other only adja cent the plunger axis whereby non-axial loading of the plunger by the bearing is minimized, and means opposing rocker thrust induced movements of the plunger including a source of fluid pressure and a non-return valve controlled passage connecting said source to the interior of the cylinder opposite the other end of the plunger.

5. Supporting and journaling means for a rocker of the stud mounted type which has an opening extending therethrough in the thrust direction, comprising a fixed stud adapted to extend through the rocker opening, a generally cup-shaped cylinder aligned with and facing one end of the stud, a head rigidly interconnecting the adjacent ends of the stud and cylinder, said head having a plurality of circumferentially spaced bores extending therethrough, pins slidably supported in said bores, a rocker bearing slidably embracing the stud and abutting one of the ends of each pin, a platform member loosely fitting the internal side walls of the cylinder and abutting the other ends of said pins, a plunger slidably fitting said cylinder walls and having a centrally extended end abutting the platform member,

said cylinder and the other end of the plunger defining an oil pressure chamber, a spring acting between the plunger and the end wall of the cylinder tending to enlarge said chamber, a chamber inlet port and a check valve operative to close said port against escape of oil from the chamber whereby movement of the plunger in response to thrust from the bearing is accommodated only in accordance with the rate of oil leakage between the plunger and said side walls of the cylinder.

6. in combination, a rocker for transmitting motion between oppositely reciprocating parts, said rocker having an opening extending therethrough in the thrust direction, rocker supporting means including a generally ring shaped bearing journaling the rocker adjacent one end of said opening, a fixed stud slidably embraced by said bearing and extending through said rocker opening, an inverted generally cup-shaped cylinder facing the end of the stud above the bearing, a head rigidly interconnecting the adjacent ends of the stud and cylinder, a plunger in the cylinder, thrust transmitting means ex- -tending through said head between the bearing and plunger, an oil drain passage extending through said head from the interior of the cylinder below the plunger, a plunger return spring biasing the plunger away from the closed end of the cylinder, an oil inlet in the closed end of the cylinder, a check valve closing said inlet against escape of oil therethrough from the cylinder, a cover member secured to the upper end of the cylinder and defining an oil reservoir opposite said inlet, and series connected passageways through said stud, head and cylinder for conducting oil to supply said reservoir.

7. The combination of claim 6, wherein the internal surface of said cylinder closed end is inclined conically upwardly toward said inlet at an angle to the cylinder axis less than the inclination from vertical of said axis during normal operation.

8. The combination of claim 6, wherein said cover member is provided with an air vent hole at the upper extremity of the reservoir, together with an air pressure openable and oil pressure closable valve controlling said vent hole comprising a stem loosely fitting and of greater length than said hole, the opposite ends of said stem having enlarged head portions circumferentially overlying the lateral extremities of said hole.

9. In combination with a rocker having an opening 2 extending therethrough in the thrust direction, supporting and journaling means for the rocker including a dashpot, a plunger movable inwardly of the dashpot in response to rocker thrust, a rocker bearing disposed oppositely of the plunger from the dashpot, thrust transmitting means extending between the bearing and plunger, and fixed supporting means for the dashpot extending through the rocker opening, said bearing being guided by said fixed means between the rocker and plunger.

10. In combination with a rocker for transmitting motion between oppositely reciprocating elements, said rocker having an opening extending therethrough in the thrust direction, rocker supporting means including a bearing journaling the rocker for oscillation about its fulcrum axis, a fixed member extending through said rocker opening and supporting and guiding said bearing for lineal movement in response to rocker thrust, means rigid with said member and defining a dashpot oppositely of the hearing from the rocker, and a plunger movable inwardly of the dashpot by the bearing in response to rocker thrust.

References Cited in the file of this patent UNITED STATES PATENTS 

